The big blank areas are (mostly) 'difficult' to habitate. Northern Canada beyond the treeline is all tundra (same with North Slope in Alaska), Africa has the Sahara in the north and Namibia/dry-as-fuck-lands in the southeast. Western China is all desert, Mongolia is all steppe or desert, Australia is mostly desert/arid, South America's got the Amazon where fish and bugs try to crawl up your wee or you can die in the deserts to the south. Greenland isn't green, Iceland barely has trees (and didnt have any at one point)--- also traditionally hard to get to. Russia has even more frozen tundra. The southern coast of the Arabian peninsula is all hot shitty desert. Western US is arid, New Zealand just fucked up, and Antarctica is as cold as my ex's heart.